In electrostatography, an image comprising a pattern of electrostatic potential (also referred to as an electrostatic latent image), is formed on a surface of an electrostatographic element wherein the latent imaged area is sufficiently conductive with respect to the un-imaged area and is then developed into a toner image by contacting the latent image with an electrographic developer. If desired, the latent image can be transferred to another surface following development. The toner image may be transferred to a receiver, to which it is fused, typically by heat and pressure.
Electrostatographic apparatus such as copiers and printers operate through a series of well known steps. These steps include: (1) charging of an insulating photoconductive surface with electrostatic charges, (2) forming an electrostatic latent image by selectively discharging areas on such surface, (3) developing the latent image with toner particles, (4) transferring the toned image to a receiver for fusing thereon, and (5) cleaning by removing residual toner in preparation for similarly reusing the same surface for another such image.
Toners contain a binder and other additives, such as colorants. Electrostatographic toners are commonly made by polymerization of a binder followed by mixing with various additives and then grinding to a desired size range. Electrostatographic apparatus used to generate the latent image is constantly subjected to wear due to mechanical abrasions. The attrition can come from various sources including toner development stations, receiving element such as paper used to transfer the latent image to, and cleaning fur brush or blade used to remove untransferred toner particles. In addition, the surface of the electrostatographic element is exposed to harmful byproducts of corona wires such as ozone and nitrous oxides. Further, any hard particle falling on the electrostatographic element surface can damage when going through a transfer or cleaning nip. Therefore it is desirable that the electrostatographic imaging element be made of highly wear and abrasion resistant ceramic materials. Unfortunately, commonly used ceramic materials such as alumina and zirconia, are highly electrically insulating in nature, which prevents these materials to be used as electrostatographic imaging element. It is desirable to have an integrated thin conductive surface on an insulative ceramic substrate and use it as an electrostatographic imaging element.
As can be readily appreciated from the discussions of the foregoing prior art problems, it is desirable to find a cost effective method that can be utilized to form a totally integrated conductive surface on an insulating ceramic substrate. The chemical composition of the laser irradiated conductive ceramic layer is akin to the insulating ceramic substrate which is irradiated, and in addition, since the conductive layer is not a coating, the integrated capacitor-like device thus produced can be used in many electronic applications more efficiently than those are currently being used. The advantage of this conductive layer is that it is not a coating or a lamination but an integral and continuous part of the substrate.
Formation of laser induced electrical conductivity is described in a German Patent No. 145,581-DD by Rolf Geisler who disclosed the surface of a ceramic material which was thermally decomposed to a conductive metal upon irradiation by a laser or an electron beam. Geisler sets forth that he forms a conductive film on an insulative ceramic body, capacitors can be produced.
Nathaniel R. Quick describes in U.S. Pat. No. 5,391,841 enhanced thermal and electrical properties of thermal sprayed ceramic coating on metal substrates for high-power integrating substrates provided by focused thermal energy sources such as laser processing. Laser induced reflow and recrystallization of ceramic material causes a purification or purging by vaporizing deleterious impurities and changing the crystalline structure while densifying the resulting structure of the ceramic layer with desired dielectric properties. Subsequent to the laser treatment a metal coating is deposited by plasma spray.
Ceramic capacitors are used widely because of their high dielectric strength and durability against heat. The most common process involves bonding thin ceramic layers or ceramic coating on metal substrates for support of the ceramic and as a means for dissipating heat generated by circuit components mounted on the circuit board thereon. However, such conventional processes do not provide the desired results. Traditionally, alumina ceramic has been used with such metals as copper, aluminum, etc. because of the ease if availability. Prior art devices described above have proven to be not that efficient because of poor bond strength between the alumina ceramic and the various metal electrodes. Further, these ceramic materials in combination with copper or aluminum electrodes have been found to be incompatible at elevated temperature operations because of the difference of thermal expansion of two dissimilar materials. Also, these devices are plagued by low dielectric properties and debonding characteristics of coatings when used at high power levels.